Low-temperature valves are extensively used in applications where control of ultra-low temperature media is required, typically with media temperatures ranging from -40°C to -196°C. These valves play a crucial role in the transportation and storage systems of liquefied gases such as natural gas, liquefied petroleum gas (LPG), and liquid nitrogen. Common types of low-temperature valves include cryogenic gate valves, cryogenic globe valves, and cryogenic ball valves. To ensure effective operation even in extreme low-temperature environments, these cryogenic valves often feature an extended bonnet design. The extended bonnet not only enhances the sealing performance of the valve but also improves its convenience in operation and maintenance.
Functions and Advantages of the Extended Bonnet
The primary function of the extended bonnet is to protect the stuffing box, preventing seal failure due to low-temperature environments. The stuffing box, as a key sealing component of low-temperature valves, directly affects the valve’s sealing and safety performance. If the stuffing box leaks, it can significantly reduce the insulation effect and potentially cause the vaporization of liquefied gases, posing a hazard.
Under low-temperature conditions, as the temperature drops further, the elasticity of the packing within the valve decreases, leading to a decline in sealing performance. Media seepage may freeze at the contact point between the packing and the valve stem, affecting the normal operation of the valve stem and even causing scratches on the packing when the stem moves up and down, leading to more severe leakage issues. To prevent this, the design of the extended bonnet ensures that the temperature around the stuffing box remains above 8°C, significantly improving the valve’s leak prevention capabilities.
The Structural Design Features
A notable advantage of the extended bonnet design is its ease of wrapping with insulation materials. In low-temperature conditions, the effective application of insulation materials can reduce cold energy loss, thereby improving the system’s energy efficiency. Additionally, the extended structure facilitates the disassembly and replacement of the valve’s main components. Typically, the main components of the valve can be quickly replaced through the bonnet without separating the entire valve body from the pipeline. This design not only simplifies the maintenance process but also effectively reduces the risk of leaks in the cold box, ensuring the overall sealing integrity of the system.
In many low-temperature facilities, process pipelines and valves are often installed within “cold boxes,” and the extended bonnet can extend through the wall of the “cold box,” facilitating operation and maintenance. When replacing the main components of the valve, it is only necessary to disassemble through the bonnet, avoiding damage to the structure of the cold box, saving maintenance time, and enhancing operational convenience.
Safety and Operational Convenience
The extended bonnet not only protects the internal structure of the valve but also ensures operational safety. Its design keeps the valve’s operating handle and stuffing box away from the low-temperature area, effectively avoiding the risk of frostbite for operators due to excessively low temperatures. At the same time, this design ensures that the stuffing box and pressure sleeve can work at room temperature, thereby extending the service life of the packing. It avoids the decline in sealing performance caused by the weakening of the packing’s elasticity at low temperatures, ensuring the long-term reliable operation of the valve.
Design Adaptation to Insulation Thickness
In low-temperature pipeline systems, the thickness of the insulation layer is usually considerable, and the design of the extended bonnet is well-suited for such thick insulation conditions. The packing gland is located outside the insulation layer, facilitating the tightening or addition of packing to the gland bolts without compromising the integrity of the insulation layer. Moreover, when selecting the bonnet length, designers need to fully consider the thickness of the insulation layer. If the insulation layer is thicker than the bonnet length, the bonnet should be appropriately extended to ensure smooth insulation construction.
Application Scenarios for Extended Bonnet Design
In some specific application scenarios, the extended design of the valve stem is particularly important. For example, buried globe valves used in natural gas pipelines or valves used in well operations, the long stem design ensures convenience and safety of operation. Additionally, for pipelines with excessively high or low temperatures, the extended valve stem can effectively protect the packing in the valve bonnet, preventing leakage issues caused by extreme temperatures. The long stem design is especially crucial in low-temperature valves, primarily to prevent ice formation at the packing and valve stem, avoiding damage and leakage due to freezing.
Maintenance Convenience
The extended bonnet not only enhances the operational stability of the valve but also greatly facilitates maintenance and replacement. Maintenance personnel can directly disassemble valve components through the bonnet and valve stem without disassembling the valve body. This not only shortens the maintenance time but also avoids affecting the entire system. This design improves the maintenance efficiency of low-temperature valves, ensuring their long-term stable operation.
The extended bonnet design of low-temperature valves fully considers the special requirements of low-temperature conditions, offering significant advantages in protecting the stuffing box, preventing leaks, and facilitating operation and maintenance. With reasonable structural design and material selection, the extended bonnet not only enhances the safety and reliability of the valve but also effectively extends its service life, making it an indispensable and important component in the design of low-temperature valves.
